Oleic acid decreases the expression of a cholesterol transport-related protein (NPC1L1) by the induction of endoplasmic reticulum stress in CaCo-2 cells

J Physiol Biochem. 2011 Jun;67(2):153-63. doi: 10.1007/s13105-010-0058-y. Epub 2010 Dec 22.

Abstract

The reported data indicate that oleic acid (OA) decreases cholesterol absorption. To explore the underlying mechanisms, the effects of OA on the expression of cholesterol transport-related proteins (NPC1L1, ABCG5/8, ACAT2, MTP) and the unfolded protein response (UPR) pathway were studied in CaCo-2 enterocytes by incubating CaCo-2 cells with taurocholate micelles or taurocholate micelles containing different concentrations of OA (0.25-1.0 mM). We show that OA effectively induces XBP1 mRNA splicing, a key component of the UPR signaling, and the expression of BiP and mature ATF6 proteins in a concentration-dependent manner, leading to the induction of endoplasmic reticulum (ER) stress and activation of the UPR. Interestingly, OA decreases NPC1L1 expression in a dose-dependent manner while it has no effects on ABCG5 and MTP mRNA level or SREBP-2, ABCG8, and ACAT2 protein level. In CaCo-2 cells treated with 1.0 mM OA, both the NPC1L1 mRNA level and the NPC1L1 protein expression in brush-border membrane fractions were decreased by 39% and 37%, respectively (P < 0.01). A dose of 1 mM dithiothreitol (DTT), a positive control for ER stress induction, also decreases NPC1L1 mRNA and protein expression by 27% and 23%, respectively (P < 0.05). Furthermore, 4-phenyl-butyric acid, an UPR inhibitor, blocks OA- and DTT-induced reduction on NPC1L1 mRNA and protein levels. The results suggest that OA down-regulates NPC1L1 mRNA and protein expression via the induction of the UPR, which may play an important role in reducing intestinal cholesterol absorption.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily G, Member 8
  • ATP-Binding Cassette Transporters / metabolism
  • Caco-2 Cells
  • Cholesterol / metabolism*
  • DNA-Binding Proteins / metabolism
  • Down-Regulation
  • Endoplasmic Reticulum / drug effects
  • Endoplasmic Reticulum / metabolism*
  • Humans
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Oleic Acid / pharmacology*
  • Protein Transport / drug effects
  • RNA, Messenger / metabolism
  • Regulatory Factor X Transcription Factors
  • Sterol O-Acyltransferase / metabolism
  • Sterol Regulatory Element Binding Protein 2 / metabolism
  • Transcription Factors / metabolism
  • X-Box Binding Protein 1

Substances

  • ABCG8 protein, human
  • ATP Binding Cassette Transporter, Subfamily G, Member 8
  • ATP-Binding Cassette Transporters
  • DNA-Binding Proteins
  • Membrane Proteins
  • NPC1L1 protein, human
  • RNA, Messenger
  • Regulatory Factor X Transcription Factors
  • Sterol Regulatory Element Binding Protein 2
  • Transcription Factors
  • X-Box Binding Protein 1
  • XBP1 protein, human
  • Oleic Acid
  • Cholesterol
  • Sterol O-Acyltransferase
  • sterol O-acyltransferase 2